This proposal concerns the use of the retina as a model system for the study of biochemical control mechanisms. Enzymes (e.g. glutamine synthetase, GS), and their possible relation to vision and general retinal metabolism are a major focus. Recent studies have shown 1) retina actively converts glutamate to glutamine; 2) uptake of cortisol (which induces GS) is age dependent and does not follow inducibility; 3) continued synthesis of GS is probably not dependent on continued presence of hormone; 4) glutamine exerts complex control on GS induction; 5) glutamate exerts negative control on GS induction and causes severe morphological damage to retina in culture. Current studies concern 1) age dependence of glutamate effect on retina; 2) mechanism of glutamate effect; 3) effect of glutamate on preformed GS; 4) effect of certain other amino acids on GS induction and preformed GS; 5) investigation of other retinal enzymes.